|M.Sc Student||Atrash Fouad|
|Subject||Characterization of the Mechanical Properties of Low-K|
Dielectric Thin Films
|Department||Department of Materials Science and Engineering||Supervisor||Dr. Dov Sherman|
Integrated Circuits performance is enhanced by the reduction of the RC constant. To reduce the resistance, copper is being used as the conductor for the ULSI interconnects. To reduce the capacitance, new low dielectric constant materials (Low-k) were recently introduced. There are several Low-k materials that are commercially available; all of them suffer from poor mechanical and adhesion properties, which are the source of many manufacturing and reliability difficulties.
The objective of this research is to characterize the biaxial elastic modulus, residual stresses in the Low-k materials, and the interfacial fracture energy of their adjacent interfaces. These were achieved by depositing metallic thin 'super-layer' which serves as a driving force for bending deformation (curvature) which is used to characterize the above mentioned properties.
The biaxial elastic modulus and the residual stresses where obtained by measuring the curvature of a self-deformed micro cantilever beams structures. A micro cantilever beams were formed out of the as-received wafer by an appropriate lithographic process; each beam contained the following stack of materials: CORAL//Cu/Ta/Si. Three types of specimens were used, each contained different thickness of CORAL, as follow: 500, 1000, 15000 nm. Three electron-beam evaporated Ti thin super-layers were deposited on the cantilever beams, their thickness was as follow: 150, 200, 250nm. The self deformation (curvature) was observed after releasing the cantilever beams from the substrate. The results indicate that the biaxial modulus is 15±2GPa, the residual stresses are 40±5MPa, they where deduced from the results of the cantilever beams' radii of curvature measurements
Measurements of the steady-state interfacial fracture energy (Gc) where done by introducing a pre-crack in the weakest interface of the multilayered beams mentioned above. The Ti super-layer served as a driving force for the crack propagation, thus the interfacial fracture energy was determined by changing the CORAL to Ti thicknesses' ratio. The results indicate that the steady state interfacial energy is 0.6-0.7 [J/m2].